Pyrolized organic layers and conductive prepregs made therewith

ABSTRACT

Pyrolized organic layers and conductive prepregs made therewith are provided.

BACKGROUND

Field

Pyrolized organic layers and conductive prepregs made therewith areprovided.

Brief Description of Related Technology

Epoxy resins with various hardeners have been used extensively in theaerospace industry, both as adhesives and as matrix resins for use inprepreg assembly with a variety of substrates.

Blends of epoxy resins with other resins are known. See e.g. U.S. Pat.No. 4,607,091 (Schreiber), U.S. Pat. No. 5,021,484 (Schreiber), U.S.Pat. No. 5,200,452 (Schreiber), and U.S. Pat. No. 5,445,911 (Schreiber).These blends appear to be potentially useful in the electronics industryas the epoxy resins can reduce the melt viscosity of oxazines allowingfor the use of higher filler loading while maintaining a processableviscosity. However, epoxy resins oftentimes undesirably increase thetemperature at which oxazines polymerize.

Ternary blends of epoxy resins are also known. See U.S. Pat. No.6,207,786 (Ishida), and S. Rimdusit and H. Ishida, “Development of newclass of electronic packaging materials based on ternary system ofbenzoxazine, epoxy, and phenolic resin,” Polymer, 41, 7941-49 (2000).

U.S. Pat. No. 8,178,606 is directed to and claims a composite structurecomprising a conductive surfacing film formed on a prepreg layup, wherethe surfacing film comprises silver flakes distributed substantiallyuniformly throughout the film in a substantially interconnected,lamellar configuration. The surfacing film of the '606 patent is formedfrom a curable thermosetting composition, which is defined to have atleast one multifunctional epoxy resin; at least one curing agentselected from aromatic primary amines, bisureas, boron trifluoridecomplexes, and dicyandiamide; at least one toughening agent having afunctional group selected from epoxy groups, carboxylic acid groups,amino groups and hydroxyl groups capable of reacting with othercomponents of the composition; non-conductive fillers; silver flakes inan amount greater than about 35 wt. %, based on the total weight of thecomposition. The surfacing film has an electrical resistivity of lessthan 500 mΩ/sq and a film weight in the range of 0.01-0.15 psf (poundsper square foot). The prepreg layup is comprised of a plurality ofprepreg layers, each of the prepreg layers being formed from a sheet offibers impregnated with a matrix material.

U.S. Patent Application Publication No. 2004/0071990 is directed to anelectrically conductive layer, comprising a continuous or discontinuous,non-conductive first phase comprising a polyimide base polymer, and adiscontinuous, conductive second phase comprising 80, 85, 90, 95, 96,97, 98, 99 or 100 weight percent carbon nanotube particles, where theweight percent of the second phase, based upon the total weight of bothphases, is in a range between any two of the following percentages:0.10, 0.20, 0.30, 0.40, 0.50, 0.75, 1.0, 2.0, 3.0, 4.0, 5.0, 10.0, 15.0,20.0, 25.0, 30.0 35.0, 40.0, 45.0, 46, 47, 48, 49, and 50%, where thelayer has a thickness between two and 500 microns, and where the layeror a precursor thereto is oriented on a molecular scale in one or moredirections to provide a surface electrical resistivity between, andincluding, any two of the following 50, 75, 100, 250, 500, 750, 1×10¹,1×10², 1×10³, 1×10⁴, 1×10⁵, 1×10⁶, 1×10⁷, 1×10⁸, 1×10⁹, 1×10¹⁰, 1×10¹¹,1×10¹², 1×10¹³, 1×10¹⁴, and 1×10¹⁵ ohms per square.

U.S. Patent Application Publication No. 2006/0052509 is directed to acarbon nanotube composition that contains a conducting polymer (a), asolvent (b) and carbon nanotubes (c).

International Patent Publication No. 2004/001107 is directed to a methodof forming carbon nanotube-filled composites using miniemulsionpolymerization. The carbon nanotubes are preferably single-walled carbonnanotubes. The carbon nanotubes are highly dispersed within andassociated with the polymer comprising the composite.

European Patent Publication No. EP 1 600 469 is directed to a carbonfiber composite material including a thermoplastic resin; carbonnanofibers dispersed in the thermoplastic resin; and dispersingparticles which promote dispersion of the carbon nanofibers in thethermoplastic resin.

International Patent Publication No. 2006/008518 is directed to aprotective device for a glazed structure, in particular an aircraftwindscreen, comprises at least one removable sacrificial sheet oftransparent composite. The composite comprises a transparent polymericfilm having on one side an electrically conductive layer formed from adispersion of electrically conductive particles and which is coated witha transparent hard coat, with the other side having adhesive layerthereon. Sheets of the composite may be arranged in a stack so that eachsheet adheres to the adjacent underneath sheet with the uppermost sheetof each stack being removable as the sheet becomes damaged and/or dirty.

International Patent Publication No. 2008/048705 is directed to surfacefilms, paints, or primers can be used in preparing aircraft structuralcomposites that may be exposed to lightning strikes. The surface filmcan include a thermoset resin or polymer, e.g., an epoxy resin and/or athermoplastic polymer, which can be cured, bonded, or painted on thecomposite structure. Low-density electrically conductive materials aredisclosed, such as carbon nanofiber, copper powder, metal coatedmicrospheres, metal-coated carbon nanotubes, single wall carbonnanotubes, graphite nanoplatelets and the like, that can be uniformlydispersed throughout or on the film. Low density conductive materialscan include metal screens, optionally in combination with carbonnanofibers.

International Patent Publication No. 2011/075344 is directed to metal-or metal alloy-coated sheet materials including, but not limited to,fabrics and veils which have a metal content of between one (1) andfifty (50) grams per square meter (“gsm”). The metal-coated sheetmaterials may be used as-is or in conjunction with prepregs, adhesivesor surfacing films to provide lightning strike protection (“LSP”) and/orbulk conductivity, among other benefits, to the resultant compositearticle. The resultant metal-coated fabric or veil is reportedly usefulas a carrier in surfacing films to impart surface conductivity; as acarrier in adhesives to form conductive adhesive-bonded joints; as aninterleaf (one or more metal-coated veils) between layers of prepreg toimpart surface and/or bulk conductivity as well as toughness; or tofabricate composite articles.

Notwithstanding the state of the technology, there is a need for newpyrolized organic layers that are particularly useful in makingconductive prepregs, which have the capacity to generate improvedconductivity without increasing the weight of the part made therefrom,and desirably decreasing the weight of the part. That need has remainedunsolved, despite the state of the art, until now.

SUMMARY

Accordingly, in broad strokes, provided herein in one aspect is apyrolized organic layer on at least a portion of a surface of which isdisposed conductive metal.

In another aspect, provided herein is a conductive prepreg, whichcomprises

A matrix resin;

Fiber; and

One or more of the pyrolized organic layer(s), as described above and inmore detail below.

In still another aspect, a method of substantially maintainingelectrical conductivity of a conductive prepreg while reducing theoverall weight of the conductive prepreg is provided. The methodincludes the steps of

Providing a matrix resin and fiber; and

Providing one or more of the pyrolized organic layer(s), as describedabove and in more detail below.

The present invention will be more fully understood by a reading of thefollowing detailed description.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 is a table showing comparative test data of prepregs made fromcarbon fiber and a matrix resin based upon epoxy or benzoxazine andconductive ply.

DETAILED DESCRIPTION

As noted above, in one aspect a pyrolized organic layer on at least aportion of a surface of which is disposed conductive metal is provided.The conductive metal disposed on the pyrolized organic layer desirablyis made from copper, silver or nickel.

The organic layer that is pyrolized to form the pyrolized organic layerdesirably should be made from polyimide. The pyrolized organic layershould also have a thickness of about 10 to 100 um, such as about 25 toabout 40 um. A commercial example of such a pyrolized polyimide is soldunder the tradename GRAPHINITY by Kaneka Corporation, Tokyo, Japan.GRAPHINITY is promoted by Kaneka as having high thermal conductivity inplanar direction—1,500 W/mk, which is more than three times that ofcopper and six times that of aluminum; being light weight—density about2 g/cm³ and available at a thickness of 25 um and 40 um; highelectromagnetric shielding effect; and extremely low water absorption.Pyrolysis is the reduction of a carbon containing material to a ringstructure of carbon similar to graphite. The degree to which thestarting material is converted to carbon ring structure will depend onthe chemical composition of the starting material, the elevatedtime/temperature exposure and the atmosphere of exposure. The pyrolysisconditions under argon atmosphere for a DuPont Kapton polyimide filmdescribed in Hu, C. Z. and Andrade, J. D., “Pyrolyzed, Conducting KaptonPolyimide: An Electrically Conducting Material”, Journal of AppliedPolymer Science, Vol. 30, 4409-4415 (1985) begins with the breaking ofbonds around 500° C. and follows with the development of an amorphouscarbon matrix at higher temperatures. The level of pyrolysis of the filmis a balance between conductivity and structural integrity needed forindustrial processes.

The conductive metal may be disposed on the pyrolized organic layer at athickness of about 1 to about 10 um, desirably about 2 to about 4 um.

In yet another aspect, a conductive prepreg is provided, which comprises

A matrix resin;

Fiber; and

One or more of the pyrolized organic layer(s).

The matrix resin used in the conductive prepreg may be chosen from oneor more epoxies, episulfides, oxetanes, thioxetanes, maleimides,nadimides, itaconimides, oxazines (such as benzoxazines), cyanateesters, oxazolines, phenolics, thiophenolics and combinations thereof.

Where the matrix resin includes as at least a portion thereof anoxazine, the oxazine may be embraced by the following structure:

where o is 1-4, X is selected from a direct bond (when o is 2), alkyl(when o is 1), alkylene (when o is 2-4), carbonyl (when o is 2), thiol(when o is 1), thioether (when o is 2), sulfoxide (when o is 2), andsulfone (when o is 2), and R₁ is selected from hydrogen, alkyl and aryl.

More specifically, the oxazine may be embraced by the followingstructure:

where X is selected from of a direct bond, CH₂, C(CH₃)₂, C=0, S, S═O andO═S═O, and R₁ and R₂ are the same or different and are selected fromhydrogen, alkyl, such as methyl, ethyl, propyls and butyls, and aryl.

The oxazine thus may be selected from any of the following exemplifiedstructures:

where R₁ and R₂ are as defined above.

Though not embraced by either oxazine structure I or II, additionaloxazines may be embraced by:

where R₁ are R₂ are as defined above, and R₃ is defined as R₁ or R₂.

Specific examples of these oxazines therefore include:

The oxazine may include the combination of multifunctional oxazines andmonofunctional oxazines. Examples of monofunctional oxazines may beembraced by the following structure:

where R is alkyl, such as methyl, ethyl, propyls and butyls.

As the oxazoline, compounds embraced by the following structure aresuitable:

where R¹, R², R³, R⁴, and X are hydrogen or as regards x a direct bondto a divalent organic radical, and m is 1.

Exemplary oxazolines have the following structure:

in which k is 0-6; m and n are each independently 1 or 2 provided thatat least one of m or n is 1; X is a monovalent or polyvalent radicalselected from branched chain alkyl, alkylene, alkylene oxide, ester,amide, carbamate and urethane species or linkages, having from about 12to about 500 carbon atoms; and R¹ to R⁸ are each independently selectedfrom C₁₋₄₀ alkyl, C₂₋₄₀ alkenyl, each of which being optionallysubstituted or interrupted by one or more —O—, —NH—, —S—, —CO—, —C(O)O—,—NHC(O)—, and C₆₋₂₀ aryl groups.

The oxazolines include 4,4′,5,5′-tetrahydro-2,2′-bis-oxazole,2,2′-bis(2-oxazoline); a 2,2′-(alkanediyl) bis [4,4-dihydrooxazole],e.g., 2,2′-(2,4-butanediyl) bis [4,5-dihydrooxazole] and2,2′-(1,2-ethanediyl) bis [4,5-dihydrooxazole]; a 2,2′-(arylene) bis[4,5-dihydrooxazole]; e.g., 2,2′-(1,4-phenylene)bis(4,5-dihydrooxazole], 2,2′-(1,5-naphthalenyl) bis (4,5-dihydrooxazole],2,2′-(1,3-phenylene) bis [4,5-dihydrooxazole), and2,2′-(1,8-anthracenyl) bis [4,5-dihydrooxazole; a sulfonyl, oxy, thio oralkylene bis 2-(arylene) [4,5-dihydrooxazole, e.g., sulfonyl bis2-(1,4-phenylene) [4,5-dihydrooxazole], thio bis 2,2′-(1,4-phenylene)[4,5-dihydrooxazole] and methylene bis 2,2′-(1,4-phenylene)[4,5-dihydrooxazole]; a 2,2′,2″-(1,3,5-arylene) tris[4,5-dihydrooxazole], e.g., 2,2′,2″-tris(4,5-dihydrooxazole]1,3,5-benzene; a poly [(2-alkenyl)4,5-hydrooxazole], e.g., poly[2-(2-propenyl)4,5-dihydrooxazole], andothers and mixtures thereof.

The oxazolines may have one or more of the following structures:

When the matrix resin includes at least in part an epoxy, in general, alarge number are suitable. The epoxy should have at least about two1,2-epoxy groups per molecule, though epoxy compounds with only oneepoxy group may also be used. The epoxy may be attached to a substratethat is saturated, unsaturated, cyclic or acyclic, aliphatic, alicyclic,aromatic or heterocyclic. Examples of suitable epoxies includepolyglycidyl ethers, prepared by reaction of epichlorohydrin orepibromohydrin with a polyphenol in the presence of alkali. Suitablepolyphenols therefor are, for example, resorcinol, pyrocatechol,hydroquinone, bisphenol A (bis(4-hydroxyphenyl)-2,2-propane), bisphenolF (bis(4-hydroxyphenyl)-methane), bisphenol S, biphenol,bis(4-hydroxyphenyl)-1,1-isobutane, 4,4′-dihydroxy-benzophenone,bis(4-hydroxyphenyl)-1,1-ethane, and 1,5-hydroxy-naphthalene. Othersuitable polyphenols as the basis for the polyglycidyl ethers are theknown condensation products of phenol and formaldehyde or acetaldehydeof the novolak resin-type.

Other epoxies suitable for use herein are the polyglycidyl ethers ofpolyalcohols or diamines. Such polyglycidyl ethers are derived frompolyalcohols, such as ethylene glycol, diethylene glycol, triethyleneglycol, 1,2-propylene glycol, 1,4-butylene glycol, triethylene glycol,1,5-pentanediol, 1,6-hexanediol or trimethylolpropane.

Still other epoxies are polyglycidyl esters of polycarboxylic acids, forexample, reaction products of glycidol or epichlorohydrin with aliphaticor aromatic polycarboxylic acids, such as oxalic acid, succinic acid,glutaric acid, terephthalic acid or a dimeric fatty acid.

And still other epoxides are derived from the epoxidation products ofolefinically-unsaturated cycloaliphatic compounds or from natural oilsand fats.

Particularly desirable are liquid epoxy resins derived from the reactionof bisphenol A or bisphenol F and epichlorohydrin. The epoxy resins thatare liquid at room temperature generally have epoxy equivalent weightsof from 150 to about 480.

Typically, the matrix resin may contain from about 25 to about 55 weightpercent, such as from about 30 to about 50 weight percent of epoxy.

The composition may include as at least a portion of the epoxy componenta reactive diluent such as a mono-epoxide (e.g., monoglycidyl ethers ofalkyl- and alkenyl-substituted phenols).

In addition to epoxy, episulfide is desirable as well, whether they arefull or partial episulfides, provided that they are in the solid state.Episulfides may be commercially available or readily prepared from thecorresponding epoxy through known synthetic methods.

As noted, the matrix resin may also include one or more of cyanateester, maleimide, nadimide, itaconimide, phenolic and/or thiophenolic.

The curing agent may be selected from nitrogen-containing compounds suchas amine compounds, amide compounds, imidazole compounds, guanidinecompounds, urea compounds and derivatives and combinations thereof.

For instance, the amine compounds may be selected from aliphaticpolyamines, aromatic polyamines, and alicyclic polyamines, such asdiethylenetriamine, triethylenetetramine, diethylaminopropylamine,xylenediamine, diaminodiphenylamine, isophoronediamine, menthenediamineand combinations thereof.

In addition, modified amine compounds, may be used, which include epoxyamine additives formed by the addition of an amine compound to an epoxycompound, for instance, novolac-type resin modified through reactionwith aliphatic amines.

The imidazole compounds may be selected from imidazole, isoimidazole,alkyl-substituted imidazoles, and combinations thereof. Morespecifically, the imidazole compounds are selected from 2-methylimidazole, 2-ethyl-4-methylimidazole, 2,4-dimethylimidazole,butylimidazole, 2-heptadecenyl-4-methylimidazole, 2-undecenylimidazole,1-vinyl-2-methylimidazole, 2-n-heptadecylimidazole, 2-undecylimidazole,1-benzyl-2-methylimidazole, 1-propyl-2-methylimidazole,1-cyanoethyl-2-methylimidazole, l-cyanoethyl-2-ethyl-4-methylimidazole,1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole,1-guanaminoethyl-2-methylimidazole and addition products of an imidazoleand trimellitic acid, 2-n-heptadecyl-4-methylimidazole, aryl-substitutedimidazoles, phenylimidazole, benzylimidazole,2-methyl-4,5-diphenylimidazole, 2,3,5-triphenylimidazole,2-styrylimidazole, 1-(dodecyl benzyl)-2-methylimidazole,2-(2-hydroxyl-4-t-butylphenyl)-4,5-diphenylimidazole,2-(2-methoxyphenyl)-4,5-diphenylimidazole,2-(3-hydroxyphenyl)-4,5-diphenylimidazole,2-(p-dimethylaminophenyl)-4,5-diphenylimidazole,2-(2-hydroxyphenyl)-4,5-diphenylimidazole,di(4,5-diphenyl-2-imidazole)-benzene-1,4,2-naphthyl-4,5-diphenylimidazole,1-benzyl-2-methylimidazole, 2-p-methoxystyrylimidazole, and combinationsthereof.

Modified imidazole compounds may be used as well, which includeimidazole adducts formed by the addition of an imidazole compound to anepoxy compound.

Guanidines, substituted guanidines, substituted ureas, melamine resins,guanamine derivatives, cyclic tertiary amines, aromatic amines and/ormixtures thereof. Examples of substituted guanidines aremethyl-guanidine, dimethylguanidine, trimethylguanidine,tetra-methylguanidine, methylisobiguanidine, dimethylisobiguanidine,tetramethyliso-biguanidine, hexamethylisobiguanidine,heptamethylisobiguanidine and cyanoguanidine (dicyandiamide).Representative guanamine derivatives include alkylated benzoguanamineresins, benzoguanamine resins andmethoxymethylethoxy-methylbenzoguanamine.

In addition to or instead of these hardeners, catalytically-activesubstituted ureas may be used. For instance,p-chlorophenyl-N,N-dimethylurea (monuron), 3-phenyl-1,1-dimethylurea(fenuron) or 3,4-dichlorophenyl-N,N-dimethylurea (diuron) arerepresentative examples.

The amount of curing agent may depend upon a number of factors,including whether the curing agent acts as a catalyst or participatesdirectly in crosslinking of the composition, the concentration of epoxygroups and other reactive groups in the composition, the desired curingrate and the like.

The curing agent should be present in an amount in the range of about0.01 to about 40 percent by weight, such as about 0.5 to about 20percent by weight, desirably about 1 to about 15 percent by weight,based on the total weight of the matrix resin.

The matrix resin may further include nanostructures constructed from aconductive material. The nanostructures are in the shape of one or moreof nanotubes, nanocubes, nanowires, nanopyramids, nanoplatelets,nanospheres and multiply twinned particles. The conductive material maybe a metal, such as copper, silver or nickel, or carbon. Examples of thenanostructures may be found in U.S. Pat. Nos. 7,585,349, 7,922,787,8,049,333 and 8,454,859.

When used, the nanostructures should be present in an amount in therange of about 0.01 to about 40 percent by weight, such as about 0.5 toabout 20 percent by weight, desirably about 1 to about 15 percent byweight, based on the total weight of the matrix resin.

The matrix resin should be used to make the conductive prepreg in anamount in the range of about 5 to about 60 percent by weight, such asabout 10 to about 50 percent by weight, desirably about 15 to about 35percent by weight, based on the total weight of the prepreg.

The fiber may be constructed from unidirectional fibers, woven fibers,chopped fibers, non-woven fibers or long, discontinuous fibers.

The fiber used in the conductive prepreg may be constructed from carbon,glass, aramid, boron, polyalkylene, quartz, polybenzimidazole,polyetheretherketone, polyphenylene sulfide, poly p-phenylenebenzobisoaxazole, silicon carbide, phenolformaldehyde, phthalate andnapthenoate.

When the fiber is constructed from glass, the glass fiber should beselected from the group consisting of S glass, S2 glass, E glass, Rglass, A glass, AR glass, C glass, D glass, ECR glass, glass filament,staple glass, T glass and zirconium oxide glass.

When the fiber is constructed from carbon, the carbon fiber should bemade from pitch, polyacrylonitrile or rayon. The carbon fiber isdesirable sized with an appropriate sizing agent, such as abenzoxazine-containing sizing agent.

Prepregs formed from fibers, which may be laid up in a layer format, andinfused with the matrix resin are also provided.

In this regard, processes for producing a conductive prepreg are alsoprovided. One such process includes the steps of (a) providing one ormore pyrolized organic layer(s); (b) providing fibers, such as in alayer format; (c) providing the matrix resin, optionally, withnanostructures dispersed thoughout; and (d) joining the pyrolizedorganic layer(s), the fibers and the matrix resin to form a conductiveprepreg assembly, and exposing the resulting conductive prepreg assemblyto elevated temperature and pressure conditions sufficient to infuse thefibers and pyrolized organic layer(s) with the matrix resin to form aconductive prepreg.

Another such process for producing a conductive prepreg, includes thesteps of (a) providing one or more pyrolized organic layer(s); (b)providing fibers; (c) providing the matrix resin in liquid form; (d)passing the pyrolized organic layer(s) and the fibers through the liquidmatrix resin to infuse the pyrolized organic layer(s) and the fiberswith the matrix resin to form a conductive prepreg assembly; and (e)removing excess matrix resin from the conductive prepreg assembly.

Still another process provides a method of substantially maintainingelectrical conductivity of a conductive prepreg while reducing theoverall weight of the conductive prepreg. The steps here include

Providing a matrix resin and fiber; and

Providing one or more pyrolized organic layer(s), where the pyrolizedorganic layer(s) demonstrate(s) an electrical conductivity of about 5 to30×10⁵ Siemens per meter at a weight that is about 10% to about 95% lessthan the amount of copper mesh required to demonstrate substantially thesame electrical conductivity.

The matrix resin should have a viscosity in the range of 1000 to 20000cps at an impregnation temperature of 160° F. to 250° F. In addition,the time within which the viscosity of the matrix resin increases by100% under the process conditions is in the range of 30 minutes to 10hours.

The conductive prepreg, particularly when formed by these processes,demonstrates electrical conductivity in the x direction of about 5 to30×10⁵ Siemens per meter. In the y direction, conductivity is about 5 to30×10⁵ Siemens per meter.

Also provided herein are cured conductive prepregs made by theseprocesses.

And provided herein are laminates comprising either: at least oneconductive prepreg according to that which is disclosed herein and anonconductive prepreg, where the nonconductive prepreg is made with amatrix resin comprising a benzoxazine resin, or at least two conductiveprepregs according to that which is disclosed herein.

The laminates may be made in a unidirectional, woven or quasi isotropicstructure.

The following examples are provided for illustrative rather thanlimiting purposes.

EXAMPLES

A matrix resin for use in making a conductive prepreg with carbon fiberwith the noted components in the specified amount is set forth in thetable below.

Component Weight % Oxazine 54 Epoxy Resin 18 Core Shell 5Epoxy-terminated epoxy adduct* 10 Diethylamine salt of 0.5trifluoromethanesulfonic acid Defoamer 0.5 RADEL 105 SFP 12 NIPOL 0.3*epoxy terminated adduct of two different epoxy materials usingbisphenol A as a linking portion.

This matrix resin was used to manufacture the control benzoxazineprepreg. The matrix resin with 2 percent by weight carbon nanotubeaddition was also used to manufacture a conductive prepreg. Both resinmatrices were impregnated into Toho IMS65 E23 (1.3% size) 24K carbonfiber to make unidirectional prepreg with fiber areal weight (“FAW”) of190 gsm and matrix resin content (“RC”) of 35% by weight.

A state of the art commercial unidirectional prepreg (epoxy prepreg soldby Cytec Corporation under the trade designation 977-2) used Toho IMS24K carbon fiber and had a FAW of 190 grams per square meter (gsm) andRC of 35% by weight. The unidirectional prepreg process provides for thecollimation of individual fiber tows that are comprised of 24,000individual fibers into a thin layer and combining with a thin film ofmatrix resin using pressure and temperature to form a resin impregnatedsheet of carbon fiber.

The laminate constructions were eight ply quasi-isotropic(+45/0/−45/90)_(s). One conductive ply was added to each laminateconstruction to demonstrate the benefits and advantages achievable bythe present invention. The conductive ply should be positioned such thatit faces the environment in which the laminate will be used. For anaircraft wing, for instance, the conductive ply should be positioned sothat it faces outward toward the environment, rather than inward towardthe center of the laminate.

The laminates were autoclave cured using a 1.7° C./minute ramp rate to atemperature of 177° C., with a 2 hour hold at that temperature and coolat rate of 1.7° C./minute to a temperature of 50° C. with 90 psiautoclave pressure.

Analysis of the conductive prepreg mechanical test data showedcompression after impact (“CAI”) of 253 Mpa and in-plane shear strength(“IPS”) of 125 Mpa. Commercial literature for the state-of-the-art epoxyprepreg Cytec 977-2 shows CAI of 262 Mpa and IPS of 101 Mpa. This datademonstrates that the mechanical performance of prepregs according tothe present invention is at least similar to, and in some cases betterthan, a state of the art epoxy prepreg.

Compression After Impact test method ASTM D7136-12, Standard Test Methodfor Measuring the Damage Resistance of a Fiber-Reinforced Polymer MatrixComposite to a Drop-Weight Impact Event and IPS test method ASTM D3518,Standard Test Method for In-Plane Shear Response of Polymer MatrixComposite Materials by Tensile Test of ±45° Laminate were used to obtainmechanical performance data.

Zone 3 lightning strike performance tested to Society of AutomotiveEngineers (SAE), APR5416, Aircraft Lightning Test Methods is shown inthe table set forth in FIG. 1. Prepregs made from carbon fiber and amatrix resin that is either based upon epoxy or benzoxazine withoutconductive ply showed low conductivity and failed zone 3 strike withlarge damage area and deep penetration into the laminate. Addition ofcopper mesh ply to carbon benzoxazine prepreg improved conductivity, andpassed strike with low laminate damage. However, weight increasedsignificantly. Replacement of the copper mesh ply with a pyrolized layerand the addition of carbon nanotube additive to the matrix resin showedthe highest conductivity, passed strike with low damage area and low plydamage. Significantly, a 95% decrease in conductive ply weight wasobserved compared to the copper mesh. Laminate conductivity increased by45% compared to the carbon nanotube containing laminate and 140%compared to the laminate with copper mesh conductive ply.

What is claimed is:
 1. A conductive prepreg, comprising A matrix resin;Fiber; and One or more pyrolized organic layer(s) on at least a portionof a surface of which is disposed conductive metal.
 2. The conductiveprepreg of claim 1 wherein the conductive metal is copper, silver ornickel.
 3. The conductive prepreg of claim 2, wherein the pyrolizedorganic layer has a thickness of about 25 to about 40 micrometers. 4.The conductive prepreg of claim 2 wherein the conductive metal isdisposed on the pyrolized organic layer at a thickness of about 2 toabout 4 micrometers.
 5. The conductive prepreg of claim 1 wherein thepyrolized organic layer is a polyimide.
 6. The conductive prepreg ofclaim 5, wherein the pyrolized organic layer has a thickness of about 25to about 40 micrometers.
 7. The conductive prepreg of claim 5 whereinthe conductive metal is disposed on the pyrolized organic layer at athickness of about 2 to about 4 micrometers.
 8. The conductive prepregof claim 1, wherein the pyrolized organic layer has a thickness of about25 to about 40 micrometers.
 9. The conductive prepreg of claim 8 whereinthe conductive metal is disposed on the pyrolized organic layer at athickness of about 2 to about 4 micrometers.
 10. The conductive prepregof claim 1 wherein the conductive metal is disposed on the pyrolizedorganic layer at a thickness of about 2 to about 4 micrometers.
 11. Theconductive prepreg of claim 1, wherein the matrix resin comprises one ormore epoxies, episulfides, oxetanes, thioxetanes, maleimides, nadimides,itaconimides, oxazines, cyanate esters, and bisoxazolines.
 12. Theconductive prepreg of claim 1, wherein the matrix resin furthercomprises nanostructures constructed from a conductive material.
 13. Theconductive prepreg of claim 12, wherein the nanostructures are in theshape of one or more of nanotubes, nanocubes, nanowires, nanopyramids,nanoplatelets, nanospheres and multiply twinned particles.
 14. Theconductive prepreg of claim 1, wherein the fiber is a member selectedfrom the group consisting of carbon, glass, aramid, boron, polyalkylene,quartz, polybenzimidazole, polyetheretherketone, polyphenylene sulfide,poly p-phenylene benzobisoaxazole, silicon carbide, phenolformaldehyde,phthalate and napthenoate.
 15. The conductive prepreg of claim 1,wherein the glass is a member selected from the group consisting of Sglass, S2 glass, E glass, R glass, A glass, AR glass, C glass, D glass,ECR glass, glass filament, staple glass, T glass and zirconium oxideglass.
 16. The conductive prepreg of claim 1, wherein the carbon fiberis made from pitch, polyacrylonitrile or rayon.
 17. The conductiveprepreg of claim 1, wherein the carbon fiber has been sized with abenzoxazine-containing sizing agent.
 18. The conductive prepreg of claim1, demonstrating electrical conductivity in the x direction of about 5to 30×10⁵ Siemens per meter.
 19. The conductive prepreg of claim 1,demonstrating electrical conductivity in the y direction of about 5 to30×10⁵ Siemens per meter.
 20. Cured conductive prepreg according toclaim
 1. 21. Laminate comprising at least one of the conductive prepregaccording to claim 1 and a nonconductive prepreg.
 22. Laminate accordingto claim 21, wherein the nonconductive prepreg is made with a matrixresin comprising a benzoxazine resin.
 23. Laminate comprising at leasttwo of the conductive prepregs according to claim
 1. 24. Laminateaccording to claim 23, in a unidirectional, woven or quasi isotropicstructure.
 25. A method of substantially maintaining electricalconductivity of a conductive prepreg of claim 1 while reducing theoverall weight of the conductive prepreg, comprising the steps of:Providing a matrix resin and fiber; and Providing a pyrolized organiclayer, wherein the pyrolized organic layer demonstrates an electricalconductivity of about 5 to 30×10⁵ Siemens per meter at a weight that isabout 10% to about 95% less than the amount of copper mesh required todemonstrate substantially the same electrical conductivity.